1. Field of Invention
This invention relates, in general, to mechanisms for finding and holding record media for properly printing thereon, preferably by a wire matrix type printer, and in particular, is related to a point-of-sale type data terminal having a wire matrix type printer and which must accommodate forms of the multi-layer type of various thicknesses, such as a bill-of-sale or sales order forms commonly used in retail sales.
2. Description of the Prior Art
The use of conventional wire matrix printers having a plurality of wires each individually actuated by a magnetic actuator, usually against a return spring, to impact a record medium to print a character; one wire printing one spot or dot of the character at a time, is old and well-known and the use of such wire matrix printers in point-of-sale terminals is also old and well-known, a typical example of which is discussed at length in the prior art U.S. Pat. No. to Waibel, 3,837,461, which issued Sept. 24, 1974, said patent having the same assignee as the present application.
The Waibel patent also disclosed a platen assembly for use in connection with such wire matrix printers which automatically accommodated either single or multiple layers of record media whose thicknesses varied and permitted various retailers to utilize different forms having one or more multiple copies for their own individual merchandising operation even though the number of layers and the layers themselves varied in thicknesses from retail outlet to retail outlet. The Waibel platen assembly automatically accommodated such forms, thus eliminating the necessity to customize each retail data terminal for each retailer.
While the platen assembly disclosed therein worked satisfactory under limited conditions, it has been found that an improvement was needed. First of all, while the platen accommodated forms of various thicknesses, it did not readily accommodate forms whose thicknesses may vary laterally, that is to say, may vary in thickness transverse the longitudinal axis of the forms, which transverse direction happens to be the same direction the matrix printer is printing. This variation can be caused by a number of things, such as either by a defect in the paper itself causing a non-uniform thickness of possibly in a fold in one of the layers.
Another need for improvement in the Waibel printer was in the cost of manufacture because of the large number of parts therein. Thus, there was a need not only to improve the performance of such a platen assembly, but also to reduce the cost, the latter being very important in the highly competitive business of point-of-sale terminals.